A fan installed at the back or front side of an automobile radiator, etc. is known front ends of whose radial blade portions are joined in one piece by a cylindrical ring. FIG. 8 illustrates an example of such a fan or a resin fan 12 in which a number of blade portions 3 are arranged radially on the outer perimeter of a boss portion 2, in which the front end edges of the blade portions 3 along the radius are connected to the inner surface of a bellmouth-shaped ring portion 1 in one piece and in which the blade portions 3, the boss portion 2 and the ring portion 1 are integrally molded from synthetic resin. The blade portions 3 have a shape twisted at a given angle relative to the plane in FIG. 8A.
A center hole 7 is provided at the center of the boss portion 2, and a motor rotary shaft is inserted into and fixed in the center hole 7.
A conventional fan with ring made of resin are manufactured by injection molding and has the drawback that the overall weight becomes heavier because of the need to make the blade portions 3, the boss portion 2 and so on as thick as or thicker than a given thickness for convenience of molding and in respect of strength.
It has also been difficult heretofore to ensure exact uniformity in thickness of all the blade portions 3, thus resulting in quality-related problems such as slight fan imbalance during rotation.
Further, there has been a possibility of resin shrinkage, deformation and other problems associated with molding during injection molding.
In order to solve the aforementioned problems, it is an object of the present invention to form in one piece a fan with ring by press-molding a single uniform metal plate. It is another object of the present invention to provide a manufacturing method thereof that ensures ease of manufacture and high quality.